A thermo-shrinkable film is used for packing material or labels for coating, binding or wrapping various containers including bottles, cans or the like, and longish objects including pipes, rods and so on, and is composed mainly of polyester.
A thermo-shrinkable film is employed for shrink (accumulative) packaging, shrink labeling and cap sealing various containers including, for example, polyethyleneterephthalte (PET) containers, polyethylene containers, glass containers and so on, using the heat shrinkability thereof.
In order to manufacture a label or the like, polymer material is continuously melted and extruded, thus preparing an unstretched film, which is then stretched to give a thermo-shrinkable film roll. The film in the roll is unwound, slit into a desired width, and then rewound into another roll. Subsequently, various characters and figures, including a product name and the like, are printed on the resulting film. After the completion of printing, the film is folded and bonded along both edges by means of, for example, solvent adhesion, to give a tubular film (in a tubing process). As such, there are cases where the order of performing the slitting process and the printing process is reversed. The tubular film thus obtained may be rewound into a roll and then unwound in subsequent procedures so that it is cut into tubular labels of a desired length, which are then further converted into bags through bonding along an edge of one opening thereof.
Subsequently, a container is clothed in the label or bag, passed, for example on a belt conveyer, through a shrinking tunnel (steam tunnel) wherein heated steam is blown causing thermal shrinkage or a shrinking tunnel (hot-air tunnel) wherein hot air is blown, to give a final product (a labeled container) having the label or bag tightly attached thereto.
However, all of the slitting process, the printing process, the rewinding process, and the unwinding process of the preparation of the label or bag are accompanied by a predetermined tension, and, in particular, in the process of unwinding the film or tubular film from the roll, the film or tubular film may be intermittently subjected to an intensive tension and thus may be strained.
In this case, the rupture of the thermo-shrinkable film may occur frequently, and such rupture is generated in film manufacturers and post-process companies of the film, for example, printers or final container manufacturers, resulting in increased defect rates of products and reduced productivity.
Also, in the printing process, non-uniform printing may occur frequently, consequently increasing the defect rates of products and deteriorating the external appearance of final products.